The present invention relates to a heat curable organopolysiloxane composition having a pot-life of at least 2 hours at ambient temperature, which can be rapidly cured using infrared radiation. More particularly, the present invention relates to heat curable platinum group metal catalyzed organopolysiloxane compositions containing an infrared radiation absorbing, or scattering, organic, inorganic or organometallic material.
Prior to the present invention, various platinum catalyzed heat curable organopolysiloxane compositions were available. Cure was effected by the addition of a silicon hydride to an alkenyl-substituted organosilicon material in accordance with a "hydrosilylation" mechanism. For example, Karstedt, in U.S. Pat. Nos. 3,714,334 and 3,775,452 assigned to the same assignee as the present invention, shows heat curable organopolysiloxane based on the use of a complex of Pt(O) and a vinylmethyl siloxane ligand as a hydrosilylation catalyst. Additional heat curable organopolysiloxane compositions employing platinum complexes, such as platinum halide complexes are shown by Ashby, U.S. Pat. No. 3,159,601 and Lamoreaux, U.S. Pat. No. 3,220,972, assigned to the same assignee as the present invention.
As shown by U.S. Pat. No. 3,445,420, the "pot life" or "working life" of heat curable organopolysiloxane compositions can be extended for at least 2 hours at 25.degree. C., based on a platinum catalyzed hydrosilylation addition reaction using an inhibitor for the platinum catalyst. The purpose of the inhibitor is to slow down the addition reaction between .tbd.SiH and C.sub.2 H.sub.3 Si.tbd. and thereby increase the work life of the organopolysiloxane mixture at low or room temperatures. Heat curable organopolysiloxane mixtures are generally composed of a base polymer consisting of a polydiorganosiloxane having chemically combined methylvinylsiloxy units which can be used in combination with a siliconhydride. Heat curable platinum catalyzed organopolysiloxane compositions employing an ethylenically unsaturated isocyanurate as an inhibitor are shown by Berger et al., U.S. Pat. No. 3,882,083 and U.S. Pat. Nos. 4,472,562 and 4,472,563 employing unsaturated acetylenic compounds as inhibitors.
In copending application Sr. No. 07/800,311, filed Nov. 29, 1991, which is incorporated herein by reference, there is shown heat curable organopolysiloxane compositions having a shelf stability exceeding 30 days at 25.degree. C., and an oven cure of less than 60 minutes at 150.degree. C. as a result of the employment of certain preformed latent platinum catalysts. The preformed latent platinum catalyst can be made by heating to a temperature of up to about 100.degree. C., a mixture consisting essentially of a zero valent platinum complex and an organic nitrogen compound, such as an azodicarboxylate, a triazoline dione, an azodiketone, or a heterocyclic aromatic nitrogen compound.
As used hereinafter the expression "one part" means a heat curable organopolysiloxane composition which is platinum group metal catalyzed, exhibiting "a shelf stability" which is defined as being able to resist a substantial increase in viscosity after exposure to accelerated aging at 50.degree. C. for several days and an oven cure of less than about 60 minutes at 150.degree. C. Platinum group metal catalysts which can be used to make one part heat curable organopolysiloxane compositions include inhibited platinum group metal catalyst, preformed platinum group metal catalysts, such as shown in copending application 07/800,311, now abandoned, or encapsulated platinum group metal catalysts such as shown by Lewis et al., U.S. Pat. Nos. 5,015,691 and 5,106,939. "Two part" heat curable organopolysiloxane compositions are heat curable organopolysiloxane compositions which upon being initially formed, have a pot life of 2 hours to 3 days under ambient conditions.
Although various one part and two part heat curable platinum catalyzed organopolysiloxane compositions having pot lives exceeding 2 hours under ambient conditions have been developed, in certain situations, there is sometimes a need to be able to substantially accelerate the cure of such heat curable silicone materials within certain specific thickness ranges. Accordingly, heat curable silicone materials are needed having an accelerated "through cure rate" which is a cure rate which can be at least 3.times. and in some instances preferably 6.times. the rate of cure achieved by conventional heating methods. The term "through cure" more particularly means the cross-sectional cure of a one part or two part heat curable platinum group metal catalyzed organopolysiloxane composition having a thickness in the range of at least about 0.1 mm to about 10 cm.